The present invention relates to a polishing device for polishing a substrate held by a polishing head as pressing the substrate against the upper surface of a polishing pad mounted on a polishing plate, and more particularly to a polishing device suitably used in polishing or global planarization of interlayer dielectrics on a semiconductor wafer.
In multilayer wiring in an LSI process, planarization of interlayer dielectrics is a very important technique. In connection with the exposure for wiring patterns on dielectrics, the depth of focus tends to be reduced in accordance with the miniaturization of wiring structures. To cope with this tendency, it is desired to establish a technique for globally planarizing steps on a wafer surface.
Various planarization techniques for interlayer dielectrics such as coating, reflowing, etching, PVD (Physical Vapor Deposition), and CVD (Chemical Vapor Deposition) have been proposed and applied. However, none of these techniques have yet realized global planarization necessary for higher miniaturization and higher integration.
Recently, chemical/mechanical polishing which applies mirror polishing to silicon wafers has been proposed for realizing global planarization with a high throughput.
FIG. 8 is a schematic side view of a polishing device according to the prior art, illustrating the configuration of a chemical mechanical polishing device used for planarization polishing of interlayer dielectrics on a semiconductor wafer.
In the polishing device shown in FIG. 8, a polishing pad 2 of a porous material is attached to the upper surface of a polishing plate (polishing bed) 1. The polishing plate 1 is horizontally supported by a plate rotating shaft 3, and is rotationally driven through the plate rotating shaft 3 in polishing.
A polishing head 4 is located above the polishing plate 1 so as to face a pad surface 2a of the polishing pad 2 on the polishing plate 1. A substrate attachment film 5 of urethane rubber of the like is attached to the lower surface of the polishing head 4, which surface is opposed to the pad surface 2a of the polishing pad 2. A substrate 6 to be polished is held through the substrate attachment film 5 to the polishing head 4 in polishing. The polishing head 4 is mounted to a head rotating shaft 8 through a universal joint 7 using a spherical sliding bearing or the like, and is rotationally driven through the head rotating shaft 8 in polishing.
A nozzle 9 for supplying a polishing agent (slurry) 11 is provided in the vicinity of the polishing head 4. The polishing agent 11 is fed from a polishing agent supply system 10 onto the pad surface 2a of the polishing pad 2.
The operation of the prior art polishing device mentioned above will now be described.
Prior to polishing, the substrate 6 such as a semiconductor wafer is attached through the substrate attachment film 5 to the lower surface of the polishing head 4. During polishing, the polishing plate 1 and the polishing head 4 are rotationally driven through the rotating shafts 3 and 8, respectively, by driving means (not shown). At this time, the polishing agent 11 is supplied from the polishing agent supply system 10 through the nozzle 9 onto the polishing pad 2. The substrate 6 held by the polishing head 4 is then pressed against the pad surface 2a under a given polishing pressure applied from pressurizing means (not shown). Accordingly, the subject surface (lower surface) of the substrate 6 is polished by the combination of a chemical polishing action by alkali contained in the polishing agent 11, and a mechanical polishing action by silica contained in the polishing agent 11.
In the prior art polishing device, even if there is a slight inclination (nonparallelisin) between the polishing plate 1 and the polishing head 4, the substrate 6 can be brought into uniform contact with the pad surface 2a by the following function of the universal joint 7. However, when the polishing pressure by the pressurizing means is set to a high value in order to respond to a high throughput, even a slight change in distribution of contact pressures in the plane of the subject surface of the substrate 6 with respect to the pad surface 2a may remarkably reduce uniformity and planarity in the plane of the subject surface of the substrate 6. Further, the distribution of contact pressures is readily varied by dimensional errors in the construction of the polishing device, malfunction of the universal joint 7 due to deposition of the polishing agent 11, misalignment between the head rotating shaft 8 and the substrate 6 in setting the substrate 6 on the polishing head 4, etc. Moreover, this polishing device cannot cope with various factors reducing uniformity of polishing in the plane of the substrate surface, such as the fact that the amount of polishing at an outer circumferential portion of the substrate is larger than that at a central portion of the substrate, because the polishing agent 11 tends to be supplied to the outer circumferential portion more smoothly than to the central portion. Additionally, in the case that the subject surface of the substrate 6 is tapering (inclined), the tapering of the subject surface is maintained by the following function of the universal joint in polishing, so that a desired level surface of the substrate 6 cannot be achieved using this polishing device.